Background Vascular complications are frequently reported after electrophysiological (EP) procedures. Ultrasound (US) guidance during femoral vein cannulation has shown to reduce vascular damage related to unsuccessful attempts. The aim of our study is to define, under ultrasound guidance, anatomical and technical predictors of successful femoral vein cannulation in a cohort of patients undergoing EP. Material and Methods From December 2015 to January 2018, 192 patients (mean age 63,1±15,9 years, M:F=118:74) undergoing EP were enrolled in the study. US-guided approach to femoral vessels cannulation was used in all subjects by four untrained operators. Femoral vein and artery depths and diameters were measured in all patients. Unsuccessful attempts (UA) and time to successful cannulation (TSC) were also calculated. Results Vein and artery depths correlated with body weight (r=0.38 and 0.39, p=0.00), body mass index (r=0.53 and 0.50, p=0.00), and body surface area (r=0.25 and 0.28, p=0.00). Interestingly, the number of UA) positively correlated with vein depth (r=0.23, p=0.01 for the right side and r=0.33, p=0.00 for the left side). Linear regression analysis showed that both vein depth (ß=0.42, p=0.001) and operator training (ß= -0.75, p=0.00) were independently associated with UA. Conclusions Anthropometric features, namely BMI and BSA, may provide information about femoral vein/artery anatomy in patients undergoing EP procedures. Patients with high BMI have deeper and larger veins, however only vein depth is a determinant of successful cannulation. Numbers of UA and TSC significantly decrease with operators training.